In a next-generation television broadcasting, MPEG-4 AAC is used, there are 2 channel, 5.1 channel and the like in terms of the number of audio channels. An apparatus which cannot reproduce 5.1 channel imposes a signal of 5.1 channel on a digital output to send the resulting signal to an audio amplifier. Multi-channel audio reproduction is carried out in the audio amplifier.
As a digital output method standards, IEC 61937-11 is applied. IEC 61937 is the standard in accordance with which compression audio data obtained by being packetized on IEC 60958-3 is transmitted, and IEC 61937-11 regulates a transmission method complying with MPEG-4 AAC. In the transmission complying with MPEG-4 AAC used in the television broadcasting, both 2 channel and 5.1 channel are compressed, and thus they are outputted at the same transmission rate as that of LPCM 48 kHz 2 channel regulated in IEC 60958-3.
Moreover, in the next-generation television broadcasting, MPEG-4 ALS is newly adopted. Then, since ALS itself is lossless compression CODEC, a data rate thereof increases. Although the data is transmitted by applying IEC 61937-10 standard, the data is outputted at the transmission rate of 96 kHz which is twice the past transmission rate.
Therefore, it is feared that at the time of switching of the transmission format from MPEG-4 AAC to MPEG-4 ALS, an allophone is generated, and head omission of a sound of content occurs. This results from that since the transmission rate is changed from 48 kHz to 96 kHz, it takes time for PLL to follow the change, and since the compression format is changed from AAC to ALS, it takes a lot of time for the audio decoder to be necessary for being changed. In addition, likewise, there is the similar fear at the time of changing from the LPCM signal having 48 kHz to the ALS signal.
Although PTL 1 describes an example in which a signal format is notified by using a command in an IEEE1394 interface, since IEC 60958 itself has no command communication path, the command cannot be applied. In addition, although PTL 2 proposes a method of notifying the following format by similarly using invalid data in the IEEE1394 interface, this is not useful in the case where a transmission frequency differs depending on the formats, and it takes time for PLL to carry out the relocking.